<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <button id="btn">
        我是一个按钮
    </button>
    <script>
        // var btn = document.getElementById('btn')
        //
        // btn.onclick = function (){
        //     alert('你还真点啊')
        // }
        a = [1,3,5,6]
        // for (i in a){
        //     console.log(a[i])
        // }
        for (var i = 0; i < a.length; i++) {
            console.log(a[i])
        }



    </script>
</body>
</html>